The present invention relates to a wheel device adapted to chairs and a chair equipped with the same. More particularly, the invention relates to a wheel device of the type in which a wheel operates under the no-load condition and retracts under the loaded condition, wherein the wheel is capable of being kept from retracting as required even under the loaded condition, and a chair to which such a wheel device is attached.
There has heretofore been placed in the market a chair for school children, in which wheel devices are attached to the lower ends of legs of the chair so that the chair can be easily moved and that the wheels retract relative to the legs when the chair has received the load due to sitting so as to prevent the wheels from working, to thereby enable school children of a relatively lower age to use the chair with safety.
The chair of this type features its convenience and has been favorably accepted in the market. As the children who are the users grow up, however, the following demands must be satisfied. For children grown up to the upper grades in school, the chair that moves on wheels while carrying a child sitting on it no longer causes danger, or the chair can be safely used by a child himself or herself. Rather, it is requested that the user be permitted to move within distances of a short range while sitting thereon. To comply with this request, the purchasers buy for their children who have grown up a new chair equipped with universal casters which are operable at all times.
In this case, however, it does not mean that the chairs used when the children were in the lower grades in school are no longer usable; i.e., adjustment of the height of the seat level permits the chairs to be used by the children who have grown up. Therefore, simply purchasing the new chairs for convenience is a wasteful expenditure. Attempts have been made to use the chair purchased when the child was of a lower age even after the child has grown up instead of buying a new one. This attempt is commercially accomplished by a chair in which fixed ground pieces and casters are replaceably attached to the lower ends of the legs of the chair so that the fixed ground pieces are attached to the lower ends of the legs for use when a child is in the lower grades in school, and that the fixed ground pieces are removed and, instead, the casters are attached when the child has grown up to the upper grades in school, whereby he or she is allowed to move over narrow distances while sitting thereon.
According to this construction, however, the chair is used without the wheel device when the child is in the lower grades in school. Except when the child is sitting, therefore, this chair is inconvenient such as when it is to be moved. In addition, the replacement operation is cumbersome. More than that, the fixed ground pieces are replaced by the casters in many cases after the chair has been used for two or three years. Therefore, the user must store the casters for years and it often happens that the casters are missing by the time when they are to be used. If the casters capable of solving such problems were developed, they can be used not only for the chairs for school children but also for chairs for persons who need care taking, chairs for use in offices and the like. In this respect, therefore it has been urged to positively solve the above-mentioned problems.
The present invention has been made in view of such circumstances. Accordingly, it is an object of the present invention to provide a novel wheel device which enables a wheel to operate at all times as required without replacement of a conventional retractable wheel device, and a novel chair equipped with such a wheel device.
In accordance with one aspect of the present invention, a wheel device is provided. The wheel device includes a wheel having an axle, a holder member for holding the wheel, an urging member, arranged between the wheel and the holder member, for constantly urging the wheel to be projected in an operable position, and a retraction permitting member adapted to permit the wheel to be retracted while overcoming the urging force of the urging member when a load is exerted in the direction of gravity on a member on which the wheel is mounted. The retraction permitting member includes a setting mechanism for setting the wheel to be in a retraction blocked state.
According to this invention, even a retractable wheel can be used so as to select the state of blocking the retraction in which the wheel is forcibly maintained to work.
In a preferred embodiment of the present invention, the holder member includes a bearing that directly supports the axle of the wheel and a casing that supports the bearing.
According to this embodiment of the invention, the holder member is constituted of the bearing and the casing for supporting the bearing. Therefore, a conventional most typical design structure can be utilized, and the wheel can be smoothly moved in a vertical direction.
In a preferred embodiment of the present invention, the holder member is mounted in the form of a universal caster on the member on which the wheel is mounted.
According to this embodiment of the invention, since the holder member is a so-called universal caster, the direction of movement is not limited.
In a preferred embodiment of the present invention, the urging member is directly disposed between the bearing and casing or substantially between the bearing and casing while another member is interposed between the bearing and casing.
According to this embodiment of the invention, a conventional most typical design structure can also be utilized.
In a preferred embodiment of the present invention, the setting mechanism includes a setting piece that acts on the bearing for the wheel so as to set between a state for permitting the retraction of the bearing and a state for blocking the retraction of the bearing, depending on the attitude of the setting piece which is set.
According to this embodiment of the invention, even a retractable wheel can be used so as to select the state for blocking the retraction in which the wheel is forcibly maintained to work.
In a preferred embodiment of the present invention, the setting piece in the setting mechanism is provided on the casing above the bearing in a manner to be rotatable about a rotational axis perpendicular to the axle, and the setting piece is provided with a retraction permission recess and a retraction blocking protrusion in portions on a side thereof adjacent to the bearing, whereby the setting piece is turned to change over the setting attitude thereof so that either the retraction permission recess or the retraction blocking protrusion is made face the upper side of the bearing.
According to this embodiment of invention, such a construction which is a so-called bayonet mechanism permits the retraction blocked state or retraction permitted state of the wheel to be selected by turning the setting piece.
In a preferred embodiment of the present invention, the setting mechanism includes a turn range-setting mechanism provided on slide surfaces of the casing and setting piece to more reliably set the retraction permitted state and the retraction blocked state.
According to this embodiment of the invention, the retraction permitted state and the retraction blocked state of the bearing can be reliably and easily changed over.
In a preferred embodiment of the present invention, the angle for turning the setting piece is 90 degrees.
According to this embodiment of the invention, the setting piece is turned 90 degrees in the bayonet-like structure to select the retraction blocked state or the retraction permitted state of the wheel.
In a preferred embodiment of the present invention, at least one of the retraction blocking protrusion of the setting piece and the bearing that comes into contact with the retraction blocking protrusion is provided with a change-over guide portion so that the setting piece is allowed to smoothly turn even in a state where the bearing is slightly entering into the retraction permission recess of the setting piece.
According to this embodiment of the invention, the setting piece can be smoothly turned even in a state where the wheel is sinking to some extent due to the own weight of the chair, i.e., even in a state-where the axle is entering to some extent into the retraction permission recess.
In a preferred embodiment of the present invention, a bearing surface and a protuberance are formed on the change-over guide portion of the bearing for stably supporting the urging member.
According to this embodiment of the invention, the urging member can be stably supported even when the urging member has moved to some extent with the turn of the setting piece.
In a preferred embodiment of the present invention, the setting piece includes a shift piece mounted on an upper end thereof at a position above the casing.
According to this embodiment of the invention, the retraction permitted state and the retraction blocked state of the wheel can be selectively and easily changed over by operating the shift piece.
In accordance with another aspect of the present invention, a chair is provided. The chair includes a seat portion, a leg portion and wheel devices constructed as described above and mounted to a lower end of the leg portion. The wheel devices are set to be in an operating state under the no-load condition, and are selectively set to be in either a non-operating state or an operating state under the loaded condition.
When the chair having such construction is used by a school child in the lower grades in school for whom safety must be maintained while he or she is sitting on it, the wheels are retracted so as to prevent the chair from being inadvertently moved. When the child grows up to the upper grades in school and the chair that moves to some extent may no longer cause danger, the chair may be so used that the wheels are maintained to work at all times.